Revealing the Real Role of Nickel Decorated Nitrogen‐Doped Carbon Catalysts for Electrochemical Reduction of CO₂ to CO

Abstract

Abstract It is widely accepted that single Ni atoms coordinated with N can highly efficiently promote CO 2 electroreduction to CO. Very recently, probably due to limited access to high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) techniques, a misleading conclusion that nitrogen‐doped carbon‐encapsulated Ni nanoparticles (NPs) possess activity similar to that of single Ni atoms was reported and was quickly followed by several similar reports. The current contribution aims to end this misleading conclusion by performing well‐designed experiments and solid theoretical analyses. For this purpose, a series of Ni/nitrogen‐doped graphite (Ni‐NG) catalysts with different dominant Ni species (single Ni atom, nitrogen‐doped carbon‐encapsulated Ni NPs, or both) are fabricated and comparatively studied for CO 2 electroreduction to CO. Two previous studies that reported nitrogen‐doped carbon‐encapsulated Ni NPs catalysts are reinvestigated, and the existence of single Ni atoms is confirmed by HAADF‐STEM. In addition, after leaching out most of the Ni NPs by a strong acid, the activity of those catalysts does not decrease but increases slightly. Density functional theory results suggest that nitrogen‐doped carbon‐encapsulated Ni NPs are highly selective for the hydrogen evolution reaction (HER) rather than for CO 2 ‐to‐CO conversion. Overall, both systematic experimental and theoretical analyses clearly reveal that the nitrogen‐doped carbon‐encapsulated Ni NPs are not active for CO 2 electroreduction.